1. Field of the Invention
The present invention relates to a throttle device which controls the intake air drawn into an internal combustion engine, hereinafter called “engine.”
2. Description of the Related Art
In recent years, a so-called electronic throttle device in which a motor drives a valve member (15) for controlling an amount of intake airflow is adopted as a throttle device for an engine of a vehicle. Japanese Patent Laid-Open Publication No. Hei 13-241336, for example, discloses an electronic throttle device like this. In the electronic throttle device disclosed therein, a driving force transmission means having a plurality of gears transmits torque generated by a motor to a valve member.
In a case where the gears transmit the torque of the motor, however, a foreign compound such as an abrasion powder is generated in the engagement portion of the gears, for example. The above throttle valve device (the throttle device), disclosed in Japanese Patent Laid-Open Publication No. Hei 13-241336, prevents the generated foreign compound from getting into the vicinity of a return spring which biases the valve member toward an opposite direction of the drive direction of the motor, for the purpose of stably controlling the valve member.
On the other hand, as described above, the motor for driving the valve member is absolutely necessary in the electronic throttle device. The motor generally has a brush and a commutator which are in slidable contact with each other. Generally, the motor is disposed in the lower portion of the throttle device, and the plurality of gears as the driving force transmission means are disposed above the motor. Accordingly, the abrasion powder generated in the engagement portion of the gears and the like falls onto the motor, so that the foreign compound tends to get into and contaminate a slidable contact portion between the brush and the commutator of the motor. The entry of the foreign compound into the slidable contact portion causes the malfunction of the motor, due to poor slidable contact between the brush and the commutator.